The invention relates to an ink feeding mechanism for ink jet printers wherein solid ink is delivered as needed and is liquified by heat to be jettable against paper to print a character.
Referring to FIG. 8, one conventional rotary-type ink jet printer, in which paper is fed in a vertical direction, will be explained. A paper cassette 1 is set vertically, and the paper is pressed by a pressing device (not shown) from the back side against a pick-up roller 2. When the pick-up roller 2 is rotated by a driving source (not shown) driven by an electric signal, a sheet of paper 3 is drawn by the pick-up roller 2, and is transfered between an insert roller (not shown) and a presser roller 4 and further between an outer shell 5 and an inner shell 6. Then, the paper 3 is transfered vertically by endless synchronized belts 9, 10 which are driven by driving pulleys 7a, 7b and 8a, 8b respectively. The driving pulley 7a, 7b, 8a, 8b are driven by a paper feed motor 17.
During the vertical movement of the paper, print head 11 of the ink jet printer rotates and jets ink from a nozzle 13 such that printing is conducted.
The print head 11 is rotated by a motor 12, and provides a plurality of nozzles 13 around the periphery of the print head 11.
A symbol F denotes a small fan to supply air to the paper 3 to quickly dry the jetted ink on the paper.
When the paper 3 is raised up to the point where it reaches a deflector 15, the lower portion of the paper 3 separates from the synchronized belts 9, 10, and, as a result, the paper 3 falls on a tray 16.
Referring to FIG. 9, an essential part of the print head 11 will be explained. A plurality of nozzles 13 are located at the periphery of the print head 11. An ink container 18 is located in a lower portion of the print head 11. A pulse generator 19 sends a signal to a piezo-electric element (not shown) provided at the nozzle 13 such that the nozzle 13 pumps up ink 21 through a feeder tube 20 and jets the ink to the paper 3 (FIG. 8) to print the required character.
An ink supply reservoir 23, wherein the solid ink is liquified, is positioned above the container 18. A rod-like level detector 22 is provided in the container 18. The level detector 22 provides a thermistor 22a and may be made of a fluorocarbon resin to protect from heat and corrosion.
When an operator puts a solid ink pellet in the reservoir 23, the solid ink will be heated by a heater 23a and be liquified and storaged. The temperature of the liquified ink is maintained at an appropriate level by a thermostat (not shown). When the ink level in the container 18 is lowered, the level detector 22 inputs a signal to a CPU (not shown). The CPU then energizes a solenoid valve 23b to open, such that the liquified ink flows from the reservoir 23 to the container 18.
Typically, ink supply reservoirs 23 are bulky and situated adjacent to the upper side of the print head 11. If four colors, namely black, blue, red, and yellow are required, four reservoirs, each with a heater 23a, a solenoid valve 23b and a feeder tube 23c, are placed in a complicated formation and the operator can face difficulty with the operation and maintenance of the unit.
Besides, since the ink container 18, the print head 11 and the ink supply reservoir 23 are located so closely in a vertical direction, heat from these parts may be accumulated and the parts may tend to be heated up to a higher temperature than desired. Thus, if the printer is operated for many hours, the ink may become deteriorated as the solvents in the ink evaporate and, as a result, the printing quality will be degraded.
In a conventional carriage-type ink jet printer, as shown in FIG. 10, a support shaft 25 is provided at a base 24, The base 24 is located beside a print head 11. An ink holder 26, having multiple areas 26b for storing solid ink 27, is placed rotatably on the support shaft 25.
A center portion of the frame 26a of the ink holder 26 is pierced by the support shaft 25. A support plate 28 is located closely under the ink holder 26. The support plate 28 provides a hole 28a such that the solid ink 27 falls down to the print head 11 when the solid ink is overlaped on the hole 28a by rotation of the ink holder 26.
Referring to FIG. 11, which is a plan view of the embodiment of FIG. 10, a sprocket 29 is provided at the lower end of the frame. One end of a lever 30 engages the sprocket 29. The lever 30 is pivoted by a support pin 31 which is attached to the print head 11. The rear end 30b of the lever 30 is pulled by a spring 32 such that the end 30a is urged to always engage with the sprocket 29.
Under the above-described conventional-type of ink feeding mechanism, when the print head 11 moves in direction of arrow A (FIG. 11), the lever 30 moves with the print head 11 but its end 30a will not mesh with the sprocket 29, so the ink holder 26 stays unmoved. On the other hand, when the print head moves in direction of arrow B, the end 30a meshes with the sprocket 29, so the ink holder 26 rotates counter-clockwise.
As the solid ink 27 overlaps on a hole 28a, the solid ink 27 falls into the print head 11 as the dotted-line solid ink 27a shows (FIG. 10).
With such an ink feeding design, if multiple colors (e g., black, blue, red, and yellow) are required, four ink holders 26 are required. However, the solid ink 27 is supplied in response to the movement of the print head 11. Thus, control of the solid ink supply is very difficult.
It is therefore an object of the invention to provide a solid-to-liquid ink printer having an improved solid ink delivery mechanism.
It is a further object of the invention to provide an improved delivery system for solid-ink pellets.